I did a couple of google searches and found different sites that have free downloads of desktop dyno. Some are different versions 2000, 2003 etc. are any of these any good?
http://www.compcams.com/Camquest/
Comp cams just released their own version for free- basically its desktop dyno 2000 but it uses their cams- it kinda helpful for comparing cams. Not the acuracy but at least the different curves ect.